A U.S. Marine assigned to the southern U.S. border fired his service weapon on duty after he was reportedly attacked.

The Marine, who was not named, alleged he was attacked by three individuals while he was inside his vehicle early Wednesday morning last week, officials told the Associated Press on Friday.

An investigation is underway, spokesman for U.S. Northern Command John Cornelio told the Associated Press. Cornelio confirmed that the Marine fired his weapon, and there were no injuries in the incident, but no other details could be provided during the active investigation.

The incident took place at a mobile surveillance camera site located near El Centro, California, about 10 miles from the U.S.-Mexico border.

The U.S. Army soldiers didn’t have enough time to request emergency assistance before they were quickly approached by the Mexican troops wielding FX-05 Xiuhcoatl military rifles, Newsweek reported at the time.

They were instructed to stand at the front of the vehicle where they were searched and disarmed. One of the Mexican soldiers removed the Army sergeant’s Beretta M9 service pistol and placed it inside the vehicle.

Officials had said the sergeant permitted the Mexican soldier to disarm them “in an attempt to de-escalate a potential volatile situation.”

The incident later prompted a review of protocol.

“There continue to be record numbers of families and children arriving predominantly from the Northern triangle countries of Guatemala, Honduras and El Salvador, with over 58,000 family members apprehended on the southern border in April,” a Department of Homeland Security official told CNN last month.

The excessive number of migrants entering the country has caused “dire concerns” due to the lack of detention space, forcing migrants to be held in temporary facilities for long periods of time.

“This is dangerously elevating the time in custody and poses serious, significant safety risks,” the official said.